Add the PyTox test suite from the v0.2.0 branch

[emdee-is]

The v0.2.0 branch which was PyTox had an excellent test suite:
https://github.com/TokTok/py-toxcore-c/blob/v0.2.0/tests/tests.py
that covered a lot of the API, and showed good examples of usage.

The current tests have almost no coverage and there are no examples of usage.

The new Cython port should incorporate the test suite from the v0.2.0 branch and any tests that aren't covered can be marked with @unittest.skip('not in API yet')